Emergency Shutdown

Emergency Shutdown

Table of contents

Objectives

Activation Mechanisms

Levels of Shutdown

Reliability and Fail safe Logic

Activation Points

Activation Hardware Features

Emergency shutdown valves

Protection Requirements

System interactions

Objective

An emergency shutdown (ESD) system is a method to rapidly cease the operation of aprocess and isolate it from incoming and outgoing connections or flows to reduce the likelihood of an unwanted event from occurring, continuing, or escalating. The aim of the ESD system is to protect personnel, afford protection to the facility, and prevent the occurrence of an environmental impact from a process event.

Objectives

Protect personnel

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Afford protection to the facility

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Prevent the occurrence of an environmental impact from a process event

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02

ACTIVATION MECHANISM

Activation Mechanism

AUTOMATIC

MANUAL

Automatic activation from confirmed fire and gas detection system alarms

Manual activation from a main facility control panel

Automatic activation from process instrumentation set points (e.g., “high-high” vibration)

Manual activation from a strategically located initiation station(s) within the facility

03

LEVELS OF SHUTDOWN

Levels of shutdown

• Total facility shutdown Catastrophic
• Unit or plant shutdown Severe
• Unit or equipment shutdown Major
• Equipment protective system Slight

• Routine (non-ESD) alarms Routine

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04

RELIABILITY AND AND FAIL SAFE LOGIC

Reability and fail safe logic

• The design of an ESD system has traditionally been based on independent and fail safe component utilization.
• ESD system performance is measured in terms of reliability and availability. Reliability is the probability a component or system will per- form its logic function under stated operating conditions for a defined time period. Availability is the probability or mean fraction to total time that a protective component or system is able to function on demand. Increased reliability does not necessarily mean increased availability.
• Reliability is a function of the system failure rate or its reciprocal, mean time between failure (MTBF). The system failure rate in non-redundant systems is numerically equal to the sum of component failure rates
• Individual components such as vessels, pumps, compressors, etc., where a backup EIV is also provided at the battery limits of the plant that is specified as fail close. The fail safe mode can be defined as the action that is taken when the ESD system is activated. Since the function of the ESD system is to place the facility in its safest mode, by definition, the ESD activation mode is the fail safe mode.

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05

ACTIVATION POINTS

Activation points

The activation points for ESD systems should be systematically arranged to provide optimum availability and afford adequate protection to the facility. The following guidelines should be considered:

• The activation points should be located a minimum of 8 m (25 ft.) away from a high hazard location but not more than 5 min away from any location within the facility
• The chosen locations should be preferably upwind from the protected hazard. Downwind sites may be affected by heat, smoke, or toxic gases.
• They should be located in the path of normal and emergency evacua- tion routes from the immediate area. In an emergency situation, person- nel may immediately evacuate and not activate emergency controls if they are located in an inconvenient location.
• Locating sites furthest from the sources of largest liquid holdups or highly probable leakage sources (i.e., the rela- tively higher hazards) is preferred.
• They should be located near other emergency devices or equipment that may need utilization during an inci- dent (deluge activation valve(s), firewater monitors, manual blowdown valves, etc.).
• The activation point should be mounted at a height that is convenient to personnel. The ergonomics of personnel access to emergency con- trols should be accommodated.
• Manned control rooms should always be provided with hardwired ESD points located on the main console, easily accessible to operators.

06

ACTIVATION HARDWARE FEATURES

Activation hardware features

Hardwired ESD activation means have traditionally been a push-in knobs or buttons. These devices have been subject to false activation as individuals can inadvertently lean on them and cause activation.

• Each activation point should be labeled with the area of coverage and provided with an identification as to which valves it operates or equipment it shuts down.
• A specific number should be assigned to each device.
• The location itself should be highly visible, preferably highlighted in contrasting colors to normal equipment housings.
• In some instances, it may be beneficial to maintain process inventories of certain process vessels until the incident actually threatens the container since the inventory of the vessel may be crucial to the restart of the facility or the contents may be highly valuable.

07

EMERGENCY SHUTDOWN VALVES

EMERGENCY SHUTDOWN VALVES

• The failure mode of ESDVs for gas processing should always fail in the closed position, since this is the only mechanism to resolve gas-fed fires or prevent explosive vapor releases and buildups.
• The valves should be provided with an automatic fail close device such as an actuator with a spring return specification.
• The ESD valves should lock in the fail safe mode once activated and be manually reset once it has been confirmed the emergency has been resolved.
• Emergency isolation devices should be arranged so that they can be fully function tested without affecting the process operation.
• This requires that a full flow bypass may be necessary at each isolation valve if flow can- not be easily interrupted.These bypass installations should be locked closed when not in service for function testing the ESDV.
• Where motor operated valves (MOVs) or air operated valves (AOVs) are selected as ESDVs, they should, as a minimum, have backup activation power sources, and the utility service lines should be highly reliable and protected.
• . It should noted that full motor operated and air operated ESDVs are not the same as fail safe spring return valves, even if frequent functional testing is undertaken.
• The reliability of an internal spring return actuator is considered better than a self-contained MOV or AOV with its own local power source and protection of cabling.

08

PROTECTION REQUIREMENTS

PROTECTION REQUERIMENTS

ESD system components that are located in areas that would be consid- ered vulnerable to fire exposures (e.g., within tank dike areas, close to pumps, compressors, etc.) should be provided with appropriate fire pro- tection measures to ensure integrity during ESD operation and during major efforts to control an incident. Actuating mechanisms may include control panels, valve actuators, air receivers instrumentation, cabling, tubing, etc.

09

SYSTEM INTERACTIONS

SYSTEM INTERACTIONS

Process facilities may exist where operations personnel may be hesitant to activate the ESD system for fear of rupturing the incoming production pipeline due to their poor construction or current conditions. This points out the fact that all mechanism that introduce a change to the normal operating configuration of the system must first be analyzed to determine what effect the proposed actions will produce. Whenever an ESD isolation valve is closed, it will stop incoming or outgoing flows that may produce instantaneous pressure variations and can detrimentally affect the process system. An analysis of measures to prevent additional consequences should be undertaken such as slower valve closing times, increasing integrity of piping systems, etc., whenever possible.

¿QUESTIONS?

Thank you very much

Sergio Villán Flores

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